As an image-forming method of forming a toner image of excellent quality with a high speed, there is known a method of forming an image which contains the steps of: developing an electrostatic latent image on an electrostatic latent image carrier with a toner supplied from a developing roller, then transferring the formed toner image to a transfer material such as paper through an intermediate transfer material member.
With respect to the intermediate transfer material used in this method, there are required the following: excellent toner transferring property from the electrostatic latent image carrier to the intermediate transfer material, and also from the intermediate transfer material to the transfer material; and cleaning property of the remaining toner after transferring to the transfer material.
In recent years, the electrophotographic image-forming method uses a variety of transfer materials. It is required adaptability to a variety of paper including not only a plain paper and an OA exclusive paper, but also a thick paper, a coat paper, and further, a paper having unevenness on the surface (hereafter, it is called as an uneven paper). In particular, an uneven paper having an embossed treatment on the surface thereof has been frequently used for a business card and a cover of a printed matter because of its specific texture.
In order to form a good secondary transfer image on a thick paper or an uneven paper, it may be used an intermediate transfer belt that can absorb the thickness or unevenness of a transfer material (a recording material) as an intermediate transfer material used for an electrophotographic image-forming apparatus. For example, by using a rubber having elasticity for an intermediate transfer material, the surface of the intermediate transfer belt will follow the thick paper or the uneven paper, and improvement of the transfer property will be expected. Patent document 1 (JP-A No. 2010-156760) discloses an endless belt using a layered rubber elastic material containing an acrylonitrile-butadiene rubber for an electrophotographic image-forming apparatus.
However, when a rubber having a double bond is selected as an elastic material, the intermediate transfer material is rapidly deteriorated in the copying apparatus.
The intermediate transfer material having an elastic layer containing a rubber having a double bond, for example, a butadiene rubber (BR), a styrene-butadiene rubber (SBR), an acrylonitrile-butadiene rubber (NBR), an isoprene rubber (IR), and a butyl rubber (IIR), has an excellent transfer property to a paper having unevenness. However, when about 10,000 sheets of prints are made, the surface of the belt will be cracked and the formed crack will be transferred to the printed image.
The reason of this was investigated, and it was found that the formed ozone in the copying apparatus was the origin of this defect. It is thought that the double bond in the rubber structure was reacted with ozone. Because the double bond was broken or cross-linked, the rubber became stiff and it was broken.
On the other hand, although a rubber having no double bond exhibits good ozone resistance, it has problems of inferior mechanical strength and high electric resistance for using as an elastic material of an intermediate transfer material.
The rubber having no double bond, such as an ethylene-propylene rubber (EPM), and an acrylic rubber (ACM), has a high electric resistance. When an electron conducting agent such as carbon black is added for the purpose of adjusting the resistance, the rubber becomes stiff. As a result, it may not be obtained an advantage of achieving high transfer property towards an uneven paper. When an electric resistance is adjusted with an ion conducting agent, the ion conducting agent will bleed out in the copying apparatus during the operation, and it will cause a problem of degradation of the image quality by contamination to the member such as a photoreceptor. In the case of an acrylic rubber (ACM) having a relatively low electric resistance, it has a low repulsion elasticity, and has a small return after passing through press sections of a cleaning member and a transfer section. As a result, the surface will undulate, and this becomes the cause of density unevenness.
As a measure to these problems, Patent document 2 (JP-A No. 2014-209176) discloses an intermediate transfer material using a heat cured substance formed with a matrix polymer containing an acrylonitrile-butadiene rubber and a multivalent polyisocyanate. However, the transfer property to an uneven paper was not sufficient.
Consequently, it is required an intermediate transfer material enabling to transfer an excellent secondary transfer image with less occurrence of stripes or unevenness to an uneven paper even after repeated usage.